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Unformatted text preview: ; bands of actin and myosin together appear darkest. Transmission-EM How Do Muscles Contract? The sliding filament mechanism of muscle contraction:
• Myosin heads can bind specific sites on actin molecules
to form cross bridges. Myosin changes conformation,
causes actin filament to slide 5–10 nm.
! Sliding Filaments! Actin and Myosin Filaments Overlap to Form Myofibrils Actin monomer! Single sarcomere! Myosin
filament! Tropomyosin! Troponin! Actin
polypeptide chain! 47.1 How Do Muscles Contract? A neuromuscular junction is the “chemical synapse”
between a motor neuron and a muscle cell.
! Muscle cells are excitable: the plasma membrane
can conduct action potentials. Acetylcholine is released by the motor neuron at
the neuromuscular junction and opens ion
channels in the motor end plate.
! Figure 44.13 Synaptic Transmission Begins with the Arrival of a Nerve Impulse! The Neuromuscular Junction acetylcholine! Skeletal muscle
terminals ! =Na+ channels! 47.1 How Do Muscles Contract? Action potentials also travel deep within muscle
fiber via T tubules.
T tubules (transverse tubules) descend into the
sarcoplasm (muscle fiber cytoplasm).
T tubules run close to the sarcoplasmic
reticulum (ER): a closed compartment that
surrounds every myofibril.
! 47.1 How Do Muscles Contract? 47.1 How Do Muscles Contract? Sarcoplasmic reticulum: • Fancy name for the endoplasmic reticulum of Actin filaments also include tropomyosin and
troponin. muscle cells. • Has Ca2+ pumps. At rest there is high concentration Troponin has three subunits: one binds actin, one
binds myosin, and one binds Ca2+. of Ca2+ in the lumen of the sarcoplasmic reticulum. • An action potential will open the Ca2+ channels, Ca2+
flows out of sarcoplasmic reticulum and triggers
interaction of actin and myosin.
! At rest, tro...
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This note was uploaded on 02/13/2014 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.
- Winter '08